1. Field of the Invention
The invention generally relates to wireless communication, and more particularly to interference cancellation in wireless communication systems.
2. Background of the Invention
Combating interference is a primary objective in virtually all wireless communication systems. For example in a cellular wireless communication system, there are typically two types of interference that are of primary concern: inter-channel interference and intra-channel interference.
Inter-channel interference occurs when multiple base stations communicating over the same frequency band interfere with each other. Intra-cell interference occurs when communication devices within a cell all communicate with the base station over the same carrier-frequency band and a common pseudo-noise carrier. In order to avoid interference between the devices, the communications from each device are coded with a covering code that allows the base station and devices operating within the cell to detect the appropriate communication signals and ignore the potentially interfering signals from other devices within the cell.
The covering codes used in the CDMA system are typically orthogonal codes. Thus, each communication device within a particular cell encodes its communications with a code that is orthogonal to the codes used by other communication devices within the cell. The orthogonal nature of the coded communications allows particular communication signals to be extracted from other communication signals using the same frequency. However, channel effects within the cell can degrade the orthogonal relationship between the coded signals, causing intra-cell interference between signals destined for different communication devices.
In addition, signals from adjacent cells can also cause interference. For example, in a CDMA system, signals in adjacent cells may use the same frequency for communication. Thus, inter-cell interference may result from communication signals in an adjacent cell, such as transmissions originating near the edge of the adjacent cell.
In conventional communication receivers, interference in a received signal is identified, and then any of various signal processing techniques is used to cancel the interference. For example, a projection operator may be used for projecting the interference out of the signal. Thus, conventional system designs attempt to apply the operator to the received signal to project out the interference and pass the desired signal. More compact and more efficient projection algorithms are required in order to reduce computational resources, memory size, processor size, etc.